1. Field of the Invention
The present invention relates to a support structure for a light quantity control unit of a lens barrel.
2. Description of the Related Art
In a lens shutter type of lens barrel, a light quantity control unit such as a shutter or a diaphragm is often supported via a lens group holding frame. Although light quantity control members such as shutter blades or diaphragm blades must be located at predetermined positions due to optical design when pictures are taken, such elements of the light quantity control unit are free from optically-imposed constraints in the lens barrel accommodated state (in which no pictures are taken), and accordingly, a reduction in length of the lens barrel can be achieved by, e.g., bringing the light quantity control unit closer to an adjacent lens group in an optical axis direction. A support structure for a shutter unit which supports the shutter unit in a manner to allow the shutter unit to move in an optical axis direction is disclosed in, e.g., Japanese Unexamined Patent Publication 2004-206115 (hereinafter referred to as Patent Document 1).
In Patent Document 1, a shutter unit is supported to be movable in an optical axis direction by a long shaft (guide shaft) elongated in the optical axis direction. In the case where such a long shaft is molded integrally with a lens holding frame into a resin-made molded component, it is conceivable that the mold used for this molding will be parted from the molded component in the axial direction of the shaft to prevent molding lines from being formed on the molded component. However, the shaft needs to be provided with a tapered surface for releasing the shaft from the mold if the shaft is long. If the outer surface of the shaft is tapered, this tapered outer surface becomes a cause of rattling or tilting, thus making it difficult to guide the shutter unit with a high degree of precision. If a metal shaft provided as a separate member from the lens holding frame is used, the precision of the guiding can be easily secured; however, the production cost increases.